Multi-purpose reactor and process for the preparation of modified bitumen

ABSTRACT

A reactor is provided for the preparation of modified bitumen, which reactor comprises a horizontal housing comprising a cylindrical wall and two side walls, wherein a bitumen inlet has been provided at or near one of the side walls of the housing and a bitumen product outlet has been provided at or near the opposite side wall of the housing, wherein a plurality of inlets for the provision of oxygen-containing gas has been provided in the cylindrical wall of the housing between the bitumen inlet and the bitumen product outlet, which multi-purpose reactor is further provided with a mixer arranged inside the housing comprising at least one rotor rotating within at least one stator having a plurality of openings. Also there is provided a process for the preparation of modified bitumen, which comprises contacting bitumen at elevated temperature and pressure with a modifier in a reactor as herein described.

The present invention relates to a multi-purpose reactor and a processfor the preparation of modified bitumen, such as blown bitumen(including catalytically blown bitumen) or polymer modified bitumen oradditive enhanced quality bitumen.

Bitumen is a viscous, non-volatile product from crude oil. It usuallyconsists of hydrocarbons and derivatives which may be aromatic and/orhave long carbon chains. It is commonly produced by refining processesafter atmospheric or in vacuum fractionation. For raising the softeningpoint of bitumen or when a bitumen having specific properties is to beproduced the bitumen may be oxidized with an oxygen-containing gas toproduce blown bitumen. The modification of the properties of bitumen byblowing can be rather slow. Further, the blowing process may behazardous since volatile hydrocarbons may be released during the processand these hydrocarbons may accumulate in any air space within thebitumen blowing apparatus.

One such apparatus has been described in U.S. Pat. No. 3,935,093. Thisknown apparatus comprises a vertical housing provided with a bitumeninlet at the bottom, agitating means at one or more positions in thehousing and an air inlet in the lower portion of the housing. This airinlet debouches below the agitating means, such that air, that is fedinto the housing, is in contact with the agitating means. Bitumen in thehousing is moved around by the action of the agitating means and theair. A dispersion container has been arranged in the lower portion ofthe housing bitumen and serves to separate an upward bitumen flow from adownward bitumen flow. The downward bitumen flow can be discharged via abitumen outlet at the bottom of the housing. The housing has furtherbeen provided with an air offtake at the upper part of the housing.

When such an apparatus is used the residence time of the bitumen mayvary since both the inlet and the outlet for bitumen are provided at thebottom of the housing. Moreover, below the air offtake an air space mayoccur in which volatile hydrocarbons may accumulate so that hazardoussituations may arise.

SU 1198094 describes an apparatus used for blowing bitumen which is acontinuous stirred reactor that also functions as a gas-liquidseparator. Bitumen enters the reactor at one end, and leaves at theother end, whilst gases are removed from the top of the reactor. Thisreactor has considerable gas space in which volatile hydrocarbons mayaccumulate. Additionally the stirrers used to mix the bitumen and airare small when compared to the volume of the bitumen in the reactor.This means that a lengthy residence time is likely to be needed toensure reaction of all the bitumen.

In order to overcome hazardous situations a tubular reactor has beenproposed in WO-A 2006/009474. In this reactor bitumen is passed along atubular path, causing the bitumen to pass through a plurality of mixersin the tubular path. Air is injected through an air inlet at one pointalong the tubular path. So, the oxygen concentration is highest at theair inlet and gradually, along the tubular path, the oxygen getsdepleted. Hence, the driving force for the reaction diminishes along thetubular path so that the reaction rate of the oxidation reaction isfurther reduced. Moreover, the tubular path involves a high pressuredrop and thereby limits the throughput capacity of bitumen.

WO-A-2009/152461 describes a method and system for manufacturingmodified asphalts. An in-line high shear mixer is used to mix oxygencontaining gas such as air with bitumen. Like in WO-A 2006/009474 air isinjected at one point. Moreover, the blown bitumen product and anyremaining oxygen is re-circulated, in some embodiments more than 50times, back to hot bitumen storage container 102. The amount of air fedback into the hot bitumen storage container may be such that it can bere-circulated to the in-line mixer (page 13, paragraph 0032). Moreover,below the air offtake in the hot bitumen storage container an air spacemay occur in which volatile hydrocarbons may accumulate so thathazardous situations may arise.

The present invention intends to overcome the deficiencies in the priorart apparatuses and processes. Accordingly, the present inventionprovides a reactor for the preparation of modified bitumen, whichreactor comprises a horizontal housing comprising a cylindrical wall andtwo side walls, wherein a bitumen inlet has been provided at or near oneof the side walls of the housing and a bitumen product outlet has beenprovided at or near the opposite side wall of the housing, wherein aplurality of inlets for the provision of oxygen-containing gas has beenprovided in the cylindrical wall of the housing between the bitumeninlet and the bitumen product outlet, which multi-purpose reactor isfurther provided with a mixer arranged inside the housing comprising atleast one rotor rotating within at least one stator having a pluralityof openings.

The reactor of the invention ensures good mixing of bitumen andoxygen-containing gas at acceptable residence times and minimises theaccumulation of volatile hydrocarbons. The reactor can also help toreduce complexity in bitumen manufacturing. Presently, only limitedcrude feedstocks can be used to produce bitumen that meets the specifiedgrades. The reactor of the invention can be used with a wide range ofcrude feedstocks, thereby increasing flexibility. The reactor of theinvention has efficient mixing and can typically be smaller thanconventional units, thereby reducing costs.

A mixer comprising at least one rotor rotating within at least onestator having a plurality of openings is commonly referred to as a highshear mixer.

High shear mixers are used for a variety of applications, such as in thepharmaceutical industry, and in manufacture of paper, in particular inapplications where it is necessary to produce a dispersion or emulsionof ingredients that do not naturally mix. In operation, the tip of therotor turns faster than the centre of the rotor, creating shear. As therotor rotates within a stator, this forms a high shear zone. The rotorand stator combined are often referred to as the mixing head orgenerator. High shear mixing has e.g. been described in ChemicalEngineering, April 2005, pp. 46-51.

For the purpose of this specification, whenever hereinafter the term“high-shear mixer” is used, that is a short hand reference to a mixercomprising at least one rotor rotating within at least one stator havinga plurality of openings.

According to a further aspect, the present invention provides use of thereactor as described herein for the purpose of modifying bitumen.

According to a further aspect, the present invention provides a processfor the preparation of modified bitumen, which comprises contactingbitumen at elevated temperature and pressure with a modifier in areactor as described herein.

A particularly advantageous feature of the reactor according to thepresent invention is that it is a multi-purpose reactor. Prior artprocesses for the modification of bitumen utilize different reactors for(i) modifying bitumen with an oxygen-containing gas, that is forpreparing so-called blown bitumen, optionally in the presence of acatalyst, and (ii) for modifying bitumen with a polymer and/or additive.

The reactor according to the present invention can advantageously beused for preparing modified bitumen such as blown bitumen, polymermodified bitumen, additive enhanced bitumen and combinations thereof,such as multigrade bitumen.

According to one preferred embodiment the reactor of the presentinvention further comprises at least one inlet for the provision ofcatalyst and/or polymer and/or additives at or near the bitumen inlet orin the cylindrical wall of the housing.

According to another preferred embodiment, the bitumen inlet is used toprovide catalyst and/or polymer and/or additives into the reactor.Typically, bitumen and catalyst and/or polymer and/or additive ispremixed with bitumen, typically in a pre-mixing tank, and fed togetherwith the bitumen into the reactor of the present invention.

Preferably, the reactor according to the present invention furthercomprises a system for heating at least part of the cylindrical wall ofthe housing arranged within or outside at least part of the cylindricalwall of the housing.

Preferably, the system for heating is a thermostatically controllingmeans, more preferably the thermostatically controlling means is ajacket for the circulation of a liquid medium or heat tracing.

Preferably, in the reactor according to the invention the plurality ofinlets for oxygen-containing gas amounts to 3 to 10 inlets.

Preferably, in the reactor according to the invention the mixercomprises 3 to 6 rotors arranged on a single rotating shaft and eachrotating within a stator having a plurality of openings.

Preferably, in the reactor according to the invention the housing isfurther provided with baffles running in a direction perpendicular tothe side walls.

As outlined above, the present invention further provides a process forthe preparation of modified bitumen. According to one preferredembodiment, the process comprises mixing bitumen at elevated temperatureand pressure, more preferably a temperature of from 160 to 300° C., evenmore preferably 200 to 300° C., and more preferably at a pressure offrom 2 to 4 bar absolute, with a modifier, wherein the modifier is anoxygen-containing gas that is provided via a plurality of inlets.

According to another preferred embodiment, the process for thepreparation of modified bitumen involves mixing the bitumen with amodifier, wherein the modifier is a polymer or an additive and thereactor is equipped with a thermostatically controlling means.Preferably, bitumen and modifier are mixed in a pre-mix tank and themixture is introduced in the reactor through the bitumen inlet.

Preferably, the process for the preparation of modified bitumen iscarried out at a temperature of from 160 to 300° C., more preferably 200to 300° C., and preferably at a pressure of from 2 to 4 bar absolute.

The reactor according to the invention allows for a high throughput andprovides for a full flow of reactants, without allowing space for gasaccumulation. The reactants may be passed through the reactor in mixedflow pattern created by the agitator. Further, for the production ofblown bitumen, optionally in the presence of a catalyst, it allows forinjection of oxygen-containing gas in a plurality of points to controlthe reaction speed. The high-shear mixer allows for creation of smallbubbles of oxygen-containing gas, and breaking of blown bitumen layersurrounding bubbles of oxygen-containing gas. For the production ofpolymer modified bitumen or additive enhanced quality bitumen, thehigh-shear mixer ensures uniform distribution of polymer or additivesrespectively.

The reactor has been provided with a bitumen inlet and a bitumen productoutlet at or near opposite side walls of the horizontal housing. It hasbeen found that it is easier to completely fill the reactor withreactants and avoid air spaces where hydrocarbon gases may accumulate,when the inlet and outlet are present at the opposite side walls.

The reactor has a bitumen product outlet. The reactor preferably has noadditional outlet for gaseous products; the gaseous products preferablyleave the reactor via the bitumen product outlet. This is preferable toprior art systems wherein there is gas space above the bitumen in thereactor and a gas outlet for removal of gaseous products. By minimisingthe gas space in the reactor, the present inventors have reduced therisk of accumulation of volatile hydrocarbons. Preferably less than 10vol % of the reactor is gas space, more preferably less than 5 vol %,most preferably less than 1 vol %.

The housing of the reactor is arranged horizontally, that is the centralaxis of the cylindrical wall is in a substantially horizontal position,preferably not more than 10° from a horizontal position, more preferablynot more than 5°, even more preferably not more than 2°. In this way airspaces are avoided where hydrocarbon gases and any remainingoxygen-containing gas may accumulate and present a safety risk.

One of the advantages of the present invention resides in the provisionof a plurality of inlets for oxygen-containing gas. In this way theconcentration of oxygen can be monitored and controlled to a desiredlevel for the production of blown bitumen, optionally in the presence ofa catalyst. The skilled person may determine the number of inletsdepending on the size of the reactor, the throughput of bitumen and thedesired oxygen level in the mixture of bitumen and oxygen-containinggas. However, it has been found that it is preferred to have from 3 to10 inlets for oxygen-containing gas in the housing.

The oxygen-containing gas can be any gas that contains molecular oxygen.Hence, it may comprise substantially pure oxygen, oxygen-enriched air,air or even oxygen-depleted air. Also other combinations of oxygen andother, preferably inert, gases, such as nitrogen or carbon dioxide, arepossible. However, it is most convenient and economic to use air asoxygen-containing gas.

The oxygen-containing gas is typically provided to the inlets foroxygen-containing gas at elevated temperature, typically in the range offrom 30 to 300° C., preferably of from 150 or 160 to 300° C., morepreferably from 200 to 300° C.

The mixer preferably comprises at least 2 rotors rotating within atleast 2 stators. More preferably the mixer comprises at least 3 rotorsrotating within at least 3 stators. Preferably, the mixer comprises atmost 20 rotors rotating within at most 20 stators.

According to a particularly preferred embodiment, the mixer comprises aseries of rotors rotating within a stator. The number of rotors perseries preferably ranges from 2 to 6. The number of stators preferablyranges from 2 to 20, more preferably 3 to 10.

Preferably, the rotor is an impeller.

The stator has a plurality of openings. The openings may be in anydesired form or shape. According to one preferred embodiment, the statoris equipped with openings that are in the form of slots. Accordingly,preferably the stator is a slotted stator. Preferably at least onerotor/stator combination is capable of breaking down lumps of solidslike polymer lumps upon introduction in the reactor.

The person skilled in the art may design the high-shear mixer inaccordance with his desires. Key design factors include the diameter ofthe rotor and/or stator, the rotational speed, the distance between therotor and the stator, the residence time of the bitumen in the housing,the number of rotor and stator combinations. As to rotor-statorcombinations also the number of rows of teeth, their angle, and thewidth of the openings between the teeth may be varied.

Preferably, the high-shear mixer comprises multiple impellers andstators on a central rotating shaft. The central rotating shaft ispreferably arranged parallel to the axis of the cylindrical wall, morepreferably along the axis. More preferably, the high-shear mixercomprises a number of series of impellers and stators on a rotatingshaft. The number of impellers preferably ranges from 2 to 6 impellersper series and from 3 to 10 series per housing. Preferably each seriesof impellers rotates within one stator.

In operation, the velocity profile differs between the bitumen at theoutside diameter of the rotor on the one hand and the bitumen at thecentre of the rotor or the shaft. Various manufacturers have developedhigh-shear mixers. Preferably, the mixing is conducted with impellersrotating at a speed of 1000 to 3500 rpm.

Preferably the diameter of the rotors is large when compared to thediameter of the horizontal housing, thereby ensuring uniform mixing ofall the bitumen in the reactor. Preferably the ratio of the diameter ofthe rotors to the diameter of the horizontal housing is at least 1:2,more preferably at least 2:3.

It is advantageous that the bitumen is passed through the reactor atmixed flow conditions. The minor amendments in the composition by theinjection of the oxygen-containing gas is assumed not to have anymaterial effect on the mixed flow of the bitumen.

The reactor is preferably provided with one or more baffles running in adirection perpendicular to the side walls. The number of baffles mayvary within relatively wide ranges. Suitably the number ranges from 2 to20 baffles, more preferably from 3 to 6.

The reactor is suitable for use as reaction vessel for the blowing ofbitumen, optionally in the presence of a catalyst, or the preparation ofpolymer modified bitumen or additive enhanced quality bitumen. Suchreactions take usually place at elevated temperatures. For theproduction of normal or catalytically blown bitumen, the contact betweenbitumen, and oxygen-containing gas is suitably conducted at atemperature of from 160 to 300° C. For the production of polymermodified bitumen or additive enhanced quality bitumen the reactor ispreferably provided with jacketed heating or heat tracing withthermostatically controlling means. In this way the reaction rate may bekept at the desired level. One advantageous and relatively simple meansto provide thermostatic control is a jacket for the circulation of aliquid medium. Such jacket is suitably surrounding the horizontalhousing.

Due to the design of the reactor the reaction can be conducted at a widerange of reaction conditions. Such conditions include at a temperatureof from 160 to 300° C. and at a pressure of from 2 to 4 bar absolute.The multi-purpose reactor and the process of the present invention areexcellently suited for producing normal or catalytically blown bitumenor polymer modified bitumen or additive enhanced quality bitumen in acontinuous manner.

The invention will be further illustrated by means of the followingFigures.

FIG. 1 shows a schematic drawing of the reactor according to the presentinvention.

FIG. 2 shows a flow scheme of a plant wherein the reactor canconveniently be used but the skilled person will understand that thisscheme can be applied as a stand-alone skid-mounted unit at depots wherebitumen is stored, handled and distributed, outside a typical refiningcomplex.

FIG. 1 shows a reactor 1 provided with a horizontal housing comprising acylindrical wall 2 and side walls 3 and 4. Side wall 3 has been providedwith a bitumen inlet 5 through which bitumen is passed into the housing.The cylindrical wall 2 has been provided with inlets 6 for theintroduction of oxygen-containing gas, such as air. In the drawing fourinlets 6 are shown, but the skilled person will understand that thenumber of inlets may vary. The cylindrical wall 2 has further beenprovided with a bitumen product outlet 7. Bitumen product outlet 7 hasbeen arranged close to the side wall 4 in order to avoid the possibilityof creating void spaces in the reactor 1. In axial direction the reactor1 has been provided with a high-shear mixer which comprises a rotatingshaft 8; a series of rotors, preferably impellers, 9; and stators 14.Each series of rotors consists in this embodiment of two rotors,preferably each series of impellers consists in this embodiment of twoimpellers. The shaft may be operated by means of an engine, e.g., anelectrical engine, preferably a single variable speed driver 15. Toavoid vortex formation in the reactor, the horizontal housing has beenprovided with baffles 10 running along the cylindrical wall 2,perpendicular to the side walls 3 and 4. In order to control thetemperature in the housing the cylindrical wall 2 has been surrounded bya jacket 11 through which a liquid, such as a heated oil, may becirculated, which liquid is fed via a feed inlet 12 and withdrawn via adischarge 13.

FIG. 2 shows a flow scheme of a bitumen modification plant. A bitumenstorage 21 provides bitumen via a line 22 when valve 23 is open. Thebitumen in line 22 is preheated in a heat exchanger 24 typically usinghot oil. It is evident that other heating equipment may be usedalternatively. Heated bitumen is passed in line 25 via a heat exchanger26, wherein the bitumen is heated further, to a reactor 28. Reactor 28is a reactor according to the invention. The bitumen in the reactor 28is contacted with air, that is provided by a compressor 29 and a line 30via a number of injection points. Bitumen product is discharged from thereactor 28 via a line 31. In a cyclone 32 the bitumen is separated fromgases and volatile hydrocarbons. The skilled person will realise thatother separation equipment may also be used instead of a cyclone, e.g. agas-liquid separator may be used. These gases and hydrocarbons arewithdrawn from the cyclone 32 via a line 33 for further handling.Suitably, these gases are sent to an incinerator (not shown). The blownbitumen is withdrawn from the cyclone 32 via a line 34. The line 34 ispassed through the heat exchanger 26 in order to heat the bitumen to betreated. The final product, i.e., blown bitumen is recovered via a line35. If desired, part of the blown bitumen may be passed via line 40 toline 22 for further treatment.

The plant also provides for the treatment of other bitumens. The reactormay be easily cleaned and subjected to a different grade of bitumen. Asan example FIG. 2 shows a pre-mix tank 36 for a different bitumen grade,e.g., polymer-modified bitumen. Such bitumen comprises a polymer,suitably an optionally hydrogenated copolymer of an aromatic compound,such as styrene, and a conjugated diene, such as butadiene or isoprene.When valve 44 is open and valves 31 and 39 are closed, bitumen is fedvia line 46 to pre-mix tank 36 and polymer is fed via line 45 to pre-mixtank 36. The mix of polymer and bitumen is fed via a line 37 and valve38 to line 27 for further treatment in reactor 28. This providesflexibility to the bitumen plant making it a multi-purpose unit. It isalso possible to add other additives such as wax, acid and othercompounds to the bitumen by injecting such compounds into the bitumen tobe treated, e.g., via pre-mixing tank and/or via line 47 to an injectionpoint provided in line 37. The treated mix of polymer and bitumen isthen sent to storage tank via line 49 and valve 48.

It is evident that FIG. 2 provides a schematic flow scheme, in whichauxiliary equipment, such as pumps, valves, some compressors, expandersand control equipment, has not been shown. The skilled person willunderstand where this auxiliary equipment is desired.

1. A reactor for the preparation of modified bitumen, which reactorcomprises: a horizontal housing comprising a cylindrical wall and twoside walls, wherein a bitumen inlet has been provided at or near one ofthe side walls of the horizontal housing and a bitumen product outlethas been provided at or near the opposite side wall of the horizontalhousing, wherein a plurality of inlets for the provision ofoxygen-containing gas has been provided in the cylindrical wall of thehorizontal housing between the bitumen inlet and the bitumen productoutlet; and a mixer arranged inside the horizontal housing comprising atleast one rotor rotating within at least one stator having a pluralityof openings.
 2. A reactor for the preparation of modified bitumen asclaimed in claim 1, further comprising at least one inlet for theprovision of catalyst and/or polymer and/or additives at or near thebitumen inlet or in the cylindrical wall of the housing.
 3. A reactorfor the preparation of modified bitumen as claimed in claim 1, furthercomprising a system for heating at least part of the cylindrical wall ofthe housing arranged within or outside at least part of the cylindricalwall of the horizontal housing.
 4. A reactor according to claim 3,wherein the system for heating is a thermostatically controlling means.5. A reactor according to claim 4, wherein the thermostaticallycontrolling means is a jacket for the circulation of a liquid medium orheat tracing.
 6. A reactor according to claim 1, wherein the pluralityof inlets for oxygen-containing gas amounts to 3 to 10 inlets.
 7. Areactor according to claim 1, wherein the mixer comprises 3 to 6 rotorsarranged on a single rotating shaft and each rotating within a statorhaving a plurality of openings.
 8. A reactor according to claim 1,wherein the housing is further provided with baffles running in adirection perpendicular to the side walls.
 9. (canceled)
 10. A processfor the preparation of modified bitumen, which comprises mixing bitumenat elevated temperature and pressure with a modifier in a reactorcomprising a horizontal housing comprising a cylindrical wall and twoside walls, wherein a bitumen inlet has been provided at or near one ofthe side walls of the horizontal housing and a bitumen product outlethas been provided at or near the opposite side wall of the horizontalhousing, wherein a plurality of inlets for the provision ofoxygen-containing gas has been provided in the cylindrical wall of thehorizontal housing between the bitumen inlet and the bitumen productoutlet; and a mixer arranged inside the horizontal housing comprising atleast one rotor rotating within at least one stator having a pluralityof openings.
 11. A process for the preparation of modified bitumen asclaimed in claim 10, wherein the modifier is an oxygen-containing gasthat is provided via a plurality of inlets.
 12. A process according toclaim 11, wherein the mixing of bitumen with oxygen-containing gas iscarried out at a temperature of from 160 to 300° C. and at a pressure offrom 2 to 4 bar absolute.
 13. A process for the preparation of modifiedbitumen as claimed in claim 10, wherein the modifier is a polymer or anadditive and the reactor is equipped with a thermostatically controllingmeans.
 14. A process for the preparation of modified bitumen as claimedin claim 13, wherein bitumen and modifier are mixed in a pre-mix tankand the mixture is introduced in the reactor through the bitumen inlet.15. A process for the preparation of modified bitumen, which comprisesmixing bitumen at elevated temperature and pressure with a modifier in areactor comprising a horizontal housing comprising a cylindrical walland two side walls, wherein a bitumen inlet has been provided at or nearone of the side walls of the horizontal housing and a bitumen productoutlet has been provided at or near the opposite side wall of thehorizontal housing, wherein a plurality of inlets for the provision ofoxygen-containing gas has been provided in the cylindrical wall of thehorizontal housing between the bitumen inlet and the bitumen productoutlet; and a mixer arranged inside the horizontal housing comprising atleast one rotor rotating within at least one stator having a pluralityof openings; and at least one inlet for the provision of catalyst and/orpolymer and/or additives at or near the bitumen inlet or in thecylindrical wall of the housing.
 16. A process for the preparation ofmodified bitumen as claimed in claim 15, wherein the modifier is apolymer or an additive and the reactor is equipped with athermostatically controlling means.